1. Field of the Invention
This invention relates to a method for mounting a segmented pre-stressed concrete tower for wind power generators and chimneys. Particularly, this application relates to a prestressed concrete tower for wind-power or heliostatic generators, particularly pre-stressed sectioned and segmented concrete tower for wind power or heliostatic generators, and its erecting method, as well as a tower section assembling support and a lifting harness for erecting the tower or chimney.
2. Description of the Related Art
Towers of several designs have been proposed for wind-power or heliostatic generators. For example, several different towers have been built, having structures based on metallic armatures; also, they have been built with tubular sections. In both cases, their height is limited because of their dimensions, the turbulence caused by the air, their strength against intense earthquakes, and their ease of building, because in many cases it is not practical for the heights presently used. Towers made of concrete using sliding formworks are also known. For example the tower of Mathis U.S. Pat. No. 5,109,953. According to such techniques, the tower is built by pouring concrete on formworks placed on the structure.
Other well known concrete structures are made of prestressed concrete. Prestressed concrete is a technique using prestressing tendons—generally of high tensile steel cable or rods—to provide a clamping load which produces a compressive stress that reinforce the concrete structure. The pre-stressed concrete encompasses pre-tensioned concrete—wherein concrete is cast around already tensioned tendons-, and post-tensioned concrete, wherein the concrete is cast around a duct and after the curing process, compression is applied through prestressing tendons introduced within such ducts.
European patent application EP-A-0 960 986 ARAND, describes a sectioned concrete tower for wind-power generators. According to this publication, prefabricated truncated conical sections are mounted using a crane to form the tower and joined together through pre-stressing tendons. According to the publication, towers of two hundred meters' height, or more, can be erected in this way. International Patent Application WO-2004/007955 WOBBEN, from ENERCON, discloses a construction system for conical sectioned towers. This publication describes the controlled manufacture of each concrete section. The concrete section includes a series of ducts for prestressing. According to WINDBLATT, THE ENERCON MAGAZINE, Huge Building Blocks, exemplar March 2001, Sep. 22, 2201, pages 8-9, it is stated that due to their dimensions, the first pre-cast sections are divided in halves. The main drawback of the ENERCON tower is that the sections are big and heavy and so that, difficult to handle. For mounting them it requires of expensive high capacity cranes. In addition if the sections are made according to Arand, some different formwork or molds parts are required for molding each tower section.
International patent application WO-2003069099 (& U.S. Pat. No. 7,160,085 & EP-1 474 579) and DE-20 2007 003 842 U (& WO-08110309) assigned to MECAL discloses a hybrid tower for wind power generators comprising: (a) a lower portion made of a sectioned (tower divided in sections) segmented (sections divided in segments) annular pre-stressed concrete structure and an upper metallic tubular portion.
MECAL (WO-2003069099), CONCRET & STEEL (WO-2006111597 & EP-1 876 3161 & ES2246734) a subsidiary of GAMESA EOLICA, and INNEO (US-2006156681 & ES-1058539U) a subsidiary of ACCIONA EOLICA disclose a cylindrical tapered tower. The mounting method has many drawbacks, for example, the tower requires very complex joints for joining the segments—see FIGS. 13a to 13d of patent WO-2003069099-. It should be noted that segments of 12 meters height and some tons weight can be easily assembled at the floor level; however at 30 meters height it is not easy to joint the segments with the required precision. In addition, the MECAL joint must be cemented which makes the erection more complex. Furthermore, the segments are made using different molds and it is probable that the segments cannot coincide. Moreover, presstressing in the inner side of the tower—as suggested by MECAL—is non recommendable since it produces weakness in the tower. Bolt connections for joining the concrete segments are also non recommendable since any movement of the tower—an earthquake, for instances—produce movement in the tower segments that can destroy such bolts. In addition, according to the description, the erection of the tower is supposed to be reach by the use of a climbing crane. The use of such crane requires that the tower be over-designed in order to support its own weight as well as the weight of crane and it is difficult to handle at high levels—more than 30 meters—.
Summarizing, the segmented concrete conical towers of the prior art, each share the following drawbacks:
a) The ENERCON, MECAL, CONCRETE & STEEL and INNEO towers are tapered having a circular cross-section. It is to say that the bottom has a higher diameter than the top of the tower. Such design requires one mold for each segment. Because there are a number of different molds, the joining of the pieces is a difficult factor, requiring complex devices to accomplish such joining.
b) Furthermore, in the case of MECAL, the concrete segments are manufactured in a facility and then transported to the building site. Because of their sizes, such segments are big and heavy. The transportation to the site of these pre-fabricated segments, which can weigh more than 60 metric tons, must be carefully planned, using thereby big cranes and flatcars adequate for their size.
With respect of the mounting methods of segmented concrete towers of the prior art, they share the following drawbacks:
a) In the case of ENERCON, CONCRETE & STEEL and INNEO towers, the erection of these sections must be done with large-capacity cranes, able to lift complete concrete tower sections. Mounting such concrete segments demands a considerable quantity of time and it is also difficult to keep the segments in an exact position to provide the required joints of the concrete segments. The mounting according to the prior art is also affected for the weather conditions, particularly the wind. Usually some time is lost by waiting the appropriate weather conditions for conducting the necessary mounting works. In addition, for mounting segments at high levels of height it is required to provide scaffolds for the working personnel as well as special security kits, which influences the cost of said erection.
b) In the case of MECAL, which uses a climbing crane, the concrete tower must be over dimensioned in order that the lower sections support the weight of the crane as well as the upper concrete segments. Furthermore, by the use of such method it is not possible to obtain the required precision joint of adjacent concrete segments.
The tower of the invention and the mounting method can also be used for heliostatic applications. A concrete tower for solar or heliostatic generation systems is disclosed in U.S. Pat. No. 4,365,618. The concrete tower of the present invention provides a better performance if compared with the metallic towers which are subjected to tremendous thermal expansion.